1. Field of the Invention
The present invention relates to a color signal conversion method and apparatus for converting a color signal of an input gamut to a color signal of an output gamut, and to a method and apparatus for generating mapping parameters.
2. Description of the Related Art
Gamut mapping is a technique that associates a certain gamut with another gamut in a uniform calorimetric system, and is known as a conventional technique for color reproduction aimed at achieving perceptual matching between images when utilizing paper types, display media, and the like that have different gamuts. A technique by which complex map conversion from a single dimension to three dimensions is carried out over plural stages (for example, see Japanese Patent Laid-Open No. 2001-94799) and a technique that realizes a gamut map by expressing gradation representing color change as a curve (for example, see Japanese Patent Laid-Open No. 2002-33929) have been proposed as such types of gamut mapping techniques.
Regarding the yellow (Y) component in particular, while there is a trend that favors pure colors for use in color printers, cyan (C) and magenta (M) components will contaminate and muddy the Y component if hue deviation occurs with the gamut map. Such muddied color is prominent in the high brightness range of the Y component, and is perceptually apparent as a change in the hue. A technique that achieves perceptually favorable color reproduction by correcting hue deviation in the input and output gamuts respectively has accordingly been proposed (for example, see Japanese Patent Laid-Open No. 2002-152536).
However, according to the above-mentioned conventional techniques, a user is required to manually adjust a large number of color conversion parameters when mapping a gamut from a monitor to a color printer. The optimal combination of parameters also depends on, among other things, the monitor and printer models, and thus it takes an inordinate amount of time for the user to determine the optimal control parameters for the gamut map.
Furthermore, because gamut maps are typically configured from maps of a plurality of stages, controlling the mapping process is difficult, and thus a high level of knowledge regarding map conversion is required if the user is to achieve the intended color reproduction. Although mapping parameters are provided in some mapping conversion processes in order to make it easier for the user to control the mapping process, it is nevertheless difficult to understand the effects of the mapping parameters and the influence they have on the overall process.
There is therefore demand for automatic adjustment functionality by which optimal mapping parameters can be obtained, so that effective and uniformly favorable gamut mapping can be realized with regard to unspecified images.